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Robby Findler wrote:<br>
I am well aware of this. I answered the original poster's message in
the context of How to Design Programs (a textbook for introductory
programming, aka HtDP), which was clearly how it was asked.
The original post did say this: <br>
How does one typically enforce such restrictions in Scheme?
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So even though the launch pad for the discussion was a program in HtDP, I was using HtDP as the basis for a question about Scheme . In the future, I will be more explicit about what I am looking for and perhaps eliminate references to HtDP and just ask a general question. In fact, if it is a general question, perhaps it is best placed on comp.lang.scheme instead of here.
The reason I asked is that I figured that a student of mine might ask me how and/or why anything is allowed in the eye-color slot and I wanted to be able to give them an authoritative answer, as well as put my mind to rest that Scheme is a good language to become religious about in my search for The One Perfect Language.